High throw power electrodeposition process

ABSTRACT

A PROCESS FOR ELECTRODEPOSITION UTILIZING A LIQUID ELECTROLYTE WHEREIN AN EXTREMELY HIGH SOLID TO LIQUID VOLUMETRIC RATIO OF SMALL DYNAMICALLY HARD PARTICLES IS INCORPORATED IN THE SYSTEM AND VIBRATORY MOTION IMPARTED TO SUCH PARTICLES IS UTILIZED TO CARRY THE ELECTROLYTE INTO THE PLATING ZONE IN CONTACT WITH ALL SURFACES OF THE ARTICLE BEING PLATED THROUGHOUT THE PERIOD OF PLATING TO GIVE AN UNUSUAL IMPROVEMENT IN THE THROWING POWER OF THE SYSTEM.

Oct. 17, 1972 N. E. wlsnom, JR

HIGH THROW POWER ELECTRODEPOSITION PROCESS Filed May 4, 1971 /n yen/0r N0rve// E. Wisdom, Jr,

/-//'s Attorney.

United States Patent Ofice Patented Oct. 17, 1972 ABSTRACT OF THE DISCLOSURE A process for electrodeposition utilizing a liquid electrolyte wherein an extremely high solid to liquid volumetric ratio of small dynamically hard particles is incorporated in the system and vibratory motion imparted to such particles is utilized to carry the electrolyte into the plating zone in contact with all surfaces of the article being plated throughout the period of plating to give an unusual improvement in the throwing power of the system.

FIELD OF THE INVENTION Electrodeposition of metal on another surface through electrochemical action has generally been a slow process. Particularly, this has been true in the production of dense, smooth, compact platings from aqueous solutions containing dissolved salts of the metal to be deposited. Even distribution of metal on contoured surfaces has been a still further problem. The present invention relates to this general field of electrodeposition.

RELATED APPLICATIONS The present application relates to a modification of the invention covered by the earlier-filed copending application of Steve Eisner, Ser. No. 102,287, filed :Dec. 29, 1970 and entitled Vibratory Process and Apparatus.

DESCRIPTION OF PRIOR ART Efforts have been made in the past to mechanically improve electrodeposited metals. The use of small amounts of impact media such as glass spheres, sand and the like, has been tried with the idea that this would mechanically beat the plate deposited and make it more dense and coherent. Examples of this approach are illustrated in U.S. Letters Pat. Nos. 712,153; 1,051,556 and 1,594,509. More recently, French 1,500,269 recognized that incorporating a relatively high volume of particles to liquid in the form of a fluidized bed caused a reduction in cell voltage at constant relatively low current densities as compared with the voltage resulting from high electrolyte flow rates only. A still more recent approach directed to the improvement of deposition rates has been the mechanical activation described and claimed in the aforementioned copending application, Ser. No. 102,287. In that case it was found that by causing a plurality of small, dynamically hard particles having a vibratory motion to completely surround or cover the surface to be plated throughout the plating cycle a unique speed-up in plating resulted so long as the ratio of the volume of particles to liquid electrolyte was high. The imparting of energy to this particular type of system by confining the particles and electrolyte within a vibrating housing or container was found to be essential. The electrolyte level was generally maintained so as to cover or nearly cover the part to be plated with the system at rest and the success of the plating required that an extremely high number of particles be present in the plating zone (generally a variation in number of not more than 5% between the system at rest or in vibration). Activating the surface as described in said application,

4 Claims Ser. No. 102,287, is described as so treating the surface being plated as to create at such surface a high tendency to utilize the current to deposit the metal in sound, adherent form rather than as powder or dendrites. The dynamically hard particles used to accomplish this were defined as acting to produce such activation through a combination of the hardness of the particles, the contact pressure of the particles on the surface of the electrodeposit and the speed at which the particles move relative to the surface of the electrodeposit during plating.

SUMMARY The present invention involves the discovery that by causing a plurality of small, dynamically hard particles having a vibratory motion to completely surround or cover the surface to be plated throughout the plating cycle as in Ser. No. 102,287, and maintaining the electrolyte level with the system at rest below the bottom surface of the part to be plated an extremely unexpected improvement in the throwing power of the system results. With this system, essentially all of the electrolyte in the plating zone during actual plating is carried into such zone on the surface of the activating particles. Achievement of as high as 1:1 throwing power ratios on recessed portions of severely contoured shapes has been found to result from this approach without the necessity for any type of conforming anode. Plating speeds were found to be at least as high and in many instances somewhat higher than for the same electrolyte used in a conventional systern.

DRAWINGS FIG. 1 is a schematic view of the preferred mode of operation of the process illustrating one type of equipment therefor.

FIG. 2 is a schematic illustration of the anode-cathode relationship shown in FIG. 1, illustrating the relative thicknesses of metal obtained by this system.

DESCRIPTION OF PREFERRED EMBODIMENTS The process of the present invention like that of Ser. No. 102,287 requires the controlled application during plating of a plurality of small activating particles to the surface or surfaces being plated. Generally, these activating particles will be very small, i.e., having an average maximum dimension of up to about A" and preferably of about /s" or less, in order to penetrate into small radius openings on the surface to be plated. The activating particles must be preferably non-conductive and insoluble in the electrolyte. For most metals a minimum dynamic particle hardness slightly greater than the hardness of the deposited metal is necessary but since higher hardnesses do not appear to produce adverse effects, it is preferred, in order to avoid experimentation, to utilize particles having a hardness of about Knoop 500 or greater.

The particles must be capable of being wet by the electrolyte with which they are used and should have a density greater than that of the electrolyte. Generally, it has been found that extremely smooth surfaced particles are not satisfactory for the present method and a coarse or rough surface having considerable micro-irregularities providing pockets for entrapping small bodies of liquid is preferred. An extremely wide variety of particulate materials may be used so long as they meet the above criteria. Suitable particles have been found to be etched glass, sand, abrasive grains (both natural and artificial), tumbling abraslves, ceramics and the like. These particles may be used alone or in blends of one or more kinds of particles with another kind.

The activating particles must be subjected to a vibratory action at all times during plating and the object or surface to be plated must be completely covered by these activating particles while plating is in progress.

In order to achieve the high throwing power of this invention, a much greater ratio of activating particles to electrolyte is required than was considered necessary in the aforementioned Ser. No. 102,287. Since the particles also have a density greater than that of the electrolyte it has been found that the only satisfactory means for imparting the required vibratory motion to such particles is by providing a container for the entire system and externally imposing a rapid vibratory motion to such container which in turn imparts the requisite motion to the particles by repeated impacts between the container walls and the enclosed particles. The motion so imparted is designed to give such particles a macro-orbit or mass rotational movement of the particles within the container and hence past the part to be plated (maintained fixed with respect to the container). The macro-orbit of the particles is in a plane roughly parallel with a cross section of the container taken normal to its longer axis. The motion also imparts micro-orbits to the particles which continue as the particles move in the macro-orbit, such micro-orbits varying depending upon the point of impact on the container wall which initiates the movement and upon impacts with other particles, but generally being quite small elliptical or circular paths. The part to be plated, as aforesaid, is maintained fixed in the sense that it is not free to be circulated in the macro-orbit of the particles. Means are provided to either fixture or anchor such part from the surface of the container or to mount such part completely independent of any contact by the mounting means with the container.

It is also necessary to provide proper electrical connections and supply means to the workpiece to be plated and to the associated anodes. Preferably the anodes are affixed to the mounting means for the workpiece although they can be independently mounted within the container if desired. The anode type, configuration and arrangement will depend upon the shape of the part to be plated. Generally, however, the anodes are preferably in the form of either thin rectangular bars or plates or in the form of rods of circular or elliptical cross section so as to minimize interference with the macro-orbit of the activating particles. Because the anodes are also contacted by the activating particles, no problems of anode passivation are encountered and the process eliminates surface roughness on the electrodeposit which may occur in conventional plating through occlusion of small bits of anode material. Whereas shaped or conforming anodes have generally been found necessary in conventional processes where high throwing power (uniform plate thickness over varying contour surfaces) was desired, such complications are not necessary with the present process although they may be employed if desired.

Commercial vibratory abrasive finishing machines are available and can be readily modified in accordance with the present invention. Typical of such commercial units is the Rampe Model VOF-Sl Vibrader.

In order to achieve the high throwing power with the present system, vibration rates between 1,100 to 1,800 cycles per minute are required with the Rampe unit mentioned above. Amplitudes of vibration for this unit should range between about A and about Other machines may vary somewhat as to both amplitude and frequency but will generally fall in about the range specified above.

Plating rates will vary, depending chiefly upon the metal being plated and upon the plating solution used, but will generally run from the same up to slightly greater than the maximum rate achievable from the same system without the activating particles present.

As indicated above, this process as well as that of Ser. No. 102,287 requires that the surface receiving the deposit be completely covered by the activating particles throughout the plating cycle. The concentration of activating particles in the present process is sufficiently high that the part to be plated or to receive the electrodeposit can only with considerable difficulty be forced into the mass of activating particles to the desired depth absent the application of vibratory force to such mass. The depth of activating particles should generally be such (with the process stopped and no vibration being applied) as to exceed the height of the surface to be plated. The electrolyte level at rest will usually be below all of the surface to be plated and will, in any event, not cover more than 25% of the surface to be plated. Generally, the volumetric ratio of activating particles to fluid electrolyte in the plating container is not less than 4:1 when using normal, solid, geometrically shaped particles such as spheres, cylinders, cubes or irregular versions thereof. Normally, the electrolyte level at rest will occupy from 5 to 20% of the height of the plating container whereas the particle level will generally be at or near of the height of such container. As in the process of Ser. No. 102,287, it is necessary that with the part in position and ready for plating, the number of particles in the plating zone does not differ by more than about 5% from such number when the system is in operation and plating is being carried out.

In operation, the small activating particles receive the vibratory motion described above by contact with the walls of the vibratory container which motion is then transferred from particle to particle within the container. The particles in the plating zone at any given time are both vibrating and also moving with respect to the part which is fixedly positioned in the container. It is estimated that each square inch area of the surface to be plated will be impacted repetitively about 500 to 150,000 times per second by these particles depending upon the frequency of vibration and the particle size. Essentially the particles, being of a very small size, form a complete layer over each surface to be plated but a layer which is moving laternally along or across each surface as Well as vibrating normal thereto. The macro-motion causes the particles to move through the electrolyte level which is below the plating zone where the particles pick up on their microroughened surfaces the electrolyte and carry it into the plating zone.

Referring now to the drawings, FIG. 1 schematically illustrates in partial cross section a vibratory abrading machine adapted to carry out the present process. Reference numeral 10 identifies the vibratory container or hopper mounted on dual drive shafts 11 which impart the vibration to container 10. A jacket 12 is provided on container 10 to permit heating the contents by passing steam through the jacket. Mounted inside container 10 is a contoured cathode member 13 which is the part tobe plated and associated non-conforming anode members 14. The cathode 13 is supported from a cover plate 16 on top of container 10 by means of a support member 15. Likewise the anodes 14 are suspended from the cover member 16. Within the container 10 and completely covering the cathodic part 13 is a mass of small, hard non-conductive activating particles 17. The electrolyte level (shown at rest) 18 is below the bottom of the contoured cathode member 13. In operation, the container 10 is set in vibration which in turn produces vibratory motion in the mass of particles 17 and electrolyte 18. The plating current is then turned on and the vibration continued throughout the plating cycle.

FIG. 2 is an enlarged sketch of the cathode-anode configuration of FIG. 1. As illustrated, the configuration, spacing and results are those described in Example 1 herein. The cathode 13 is a 1%" wide strip of mild steel, 0.025" thick which has been uniformly finished to a micro-inch value of 14-16 R.M.S. This strip is bent into the configuration shown with the three vertical sections each about 1 /2" long and the two horizontal sections about 1" long. The last 1 /2 of the piece is bent up at approximately a 45 angle to the vertical to provide a shielded section F. The anodes 14 are spaced at an equal distance from the outermost portion on each side of the cathode member 13. As illustrated, this distance is 2". The three vertical sections have been identified with letters--A, D and E representing the sides of these sections closest to the anodes 14 while B, C and F represent the opposite surfaces of such sections respectively, each of which is approximately 1" further from an anode surface than its opposite surface using the nickel bath described in Example 1, measurement of metal thickness deposited on the cathode 13 by the present process gave the ratios indicated on the drawing. A similar cathode-anode set-up in the same bath where the electrolyte level was above the cathode and no abrasive was present (and the system was maintained without electrolyte motion) gave ratios as follows:

Example 1 A plating solution was prepared having the composition: 40 oz./gal. NiSO -6H O; 8 oz./gal. NiCl -6H O; and oz./gal. H BO A quantity of 2.2 liters of this solution was placed together with 50 pounds (volume-12 liters) of a sintered bauxite activating medium with average particle diameter- (Tumblex XM30, product of Norton Corporation, made as described in US. Pat. No. 3,079,243) into a minitub of /2 cubic foot capacity adapted to fit into the larger main tub of a Rampe Model VOF-51 Vibrader (John Rampe, Inc., Cleveland). The cathode and anodes as shown in FIG. 2 were fixed in approximately the center of the minitub by attachment to a framework rigidly attached to the main tub. The anodes Were made of sheet nickel, and the three electrodes were arranged along the long axis of the tub so that the macro-orbit of the activating particles produced by vibrating the machine was in a plane approximately perpendicular to the line joining the three electrodes. The electrodes were fixed so that the bottom of the cathode was about 3" from the bottom of the tub, and the level of electrolyte (with the tub at rest) was about 2" above the bottom of the tub.

The mixture of electrolyte and activating media was heated to a temperature of 1401-5" F. and maintained in that range during plating. The machine was set in vibratory motion at 1,550 cycles per minute with a vibration amplitude of A current equivalent to 70 amps per square foot (ASF) of exposed cathode surface was applied for minutes while vibration. was maintained. After plating, the cathode was removed and rinsed. The thickness of the plate at various points on the surface was measured with a Dermitron machine, with thickness ratios at various points as given in FIG. 2. Actual plate thickness was 0.5 mil at point D or E as indicated in FIG. 2. The plate was more highly reflective and generally more attractive in appearance than plate deposited from the same solution by conventional electrolysis without activating particles.

Example 2 All conditions were arranged as in Example 1, except that the vibration frequency used was 1,300 c.p.m. The plate thickness ratios obtained were:

Example 3 All conditions were arranged as in Example 1, except that only 1.7 liters of electrolyte were used, giving a layer of electrolyte at rest-% above the bottom of the tub. (The height of electrolyte is not proportional to the quantity introduced because of considerable retention of electrolyte by the activating particles.) The thickness of plate resulting was essentially the same as in Example 1.

Example 4 A plating solution was prepared containing 300 gm./l. CuSO .SH O, gm./l. H 80 and 0.5 vol. percent UBAC #1, a brightening-levelling agent manufactured by The Udylite Corporation. Two gallons of this solution were introduced together with 410 lbs. (volume -15 gallons) of Tumblex XM-30 into the large tub of the Rampe Vibrader described in Example 1. A layer of electrolyte about 1 /2" above the bottom of the tub resulted. Electrodes arranged as in Example 1 (except that the anodes were of copper rather than nickel) were fixed in the tub with the bottom of the cathode about 3" above the bottom of the tub. Electrolyte and Tumblex were at ambient temperature; the cathode was first given a conventional copper strike in a copper cyanide bath to promote adhesion of the copper deposit. Vibration at 1,550 c.p.m. was commenced and current was applied equivalent to ASF for 10 minutes. The cathode was removed and rinsed, and its plate thickness measured (Kocur tester) at the several points as indicated in FIG. 2. Ratios obtained were:

When the same plating solution was used with the same electrode in a conventional manner (no activating particles or agitation of solution, electrodes immersed in solution), the rates of plate thickness obtained were:

Example 5 All conditions were arranged as in Example 4, except that the vibration frequency was 1,400 c.p.m. and the plating time 5 minutes. Plate thickness ratios obtained were:

A:B= (not measured) C:D=1.2:1 E:F=2.5:1

Example 6 All conditions were arranged as in Example 4, except that 8 gallons of electrolyte were used, so that the electrolyte covered the surface of the cathode even when it was at rest. The tub was vibrated at 1,500 c.p.s. and plating current was applied at 140 ASF. Ratios of plate thickness obtained were:

Thus when the electrolyte level is high, throwing power is not nearly so good as when lower electrolyte volumes are used as described herein.

Example 7 All conditions were arranged as in Example 1, except that the current density applied was 50 ASP and the vibration frequency 1,500 c.p.s. Plate thickness ratios obtained were:

The reasons for the improved throwing power of this process are not known with any degree of certainty from a theoretical standpoint. Conventional plating theory would indicate that the results achieved must involve other than normal throwing power considerations. Not only has the process been able to produce the essentially equal thicknesses of metal on surfaces positioned at varying distances from the anodes illustrated in Examples 1, 3, 4 and 7 above, but it has been possible to put more metal on the recessed portion than at the closer projecting surfaceas illustrated in Examples 2 and 5. The system appears to Work with all plating bath compositions from which plate can be obtained by conventional methods. Probably because of the cleaning action of the activating particles, the pre-treatment of the cathode is much less critical with this process than with conventional methods.

In addition to the obvious value inherent in saving excess metal deposited, the present process presents very great savings potential in the area of high value electrolytes in that the total volume of electrolyte required is extremely smalleliminating the need for high dollar investment in large volume electrolyte capacity as is required in conventional processes.

I claim:

1. An electrodeposition process for plating metal on the surfaces of a part which comprises:

(a) providing in a container for an electrodeposition system a supply of fluid electrolyte and at least a four times greater volume of small, dynamically hard, activating particles capable of being Wet by the electrolyte;

(b) so positioning the part to be plated below the level of the activating particles that with the container at rest only up to 25% f the surfaces of said part to be plated are within said fluid electrolyte;

(c) imposing a vibratory motion at a frequency of at least about 1,100 cycles per minute on said container to initiate a movement of said particles within said container, said movement causing said supply of fluid electrolyte to wet the surfaces of substantially all of said activating particles; and

(d) initiating an electrodeposition reaction within said moving surface-wetted mass of particles while said particles repetitively contact the surfaces of said part to mechanically activate such surfaces.

2. A process as in claim 1 wherein essentially all of said surfaces of said part are out of contact with said electrolyte with the container at rest and essentially all of the electrolyte contacting said surfaces during the electrodeposition reaction is carried in on the surfaces of said particles.

3. A process as in claim 1 wherein the number of particles immediately adjacent said surfaces of said part during the imposition of said vibratory motion on said container does not differ by more than about 5% from the number of particles immediately adjacent such surfaces in the absence of such vibratory motion.

4. A process as in claim 1 wherein said particles have a micro-roughened surface.

References Cited UNITED STATES PATENTS 3,523,834 8/1970 Hcwins 148-6.15

1,214,271 1/1917 Bugbee 204DIG 10 1,051,556 l/l913 Consigliere 204DIG 10 3,201,273 8/1965 Maker et al 204DIG l0 FOREIGN PATENTS 1,500,269 9/1967 France 204DIG 10 JOHN H. MACK, Primary Examiner R. J. FAY, Assistant Examiner US. Cl. X.R.

20423, 36, 273, 274, DIG 10 

